Mill for comminuting solid material



D. DJTAYLOR MILL FOR COMMINUTING SOLID MATERIAL A rii 21, 1959 FiledApril '7, 1955 .DnN/EL. DWIGHT' film 402,

United States Patent MILL FOR COMlVIlNUTING SOLID MATERIAL Daniel DwightTaylor, Altadena, Calif, assignor to Beckman Instruments, Inc.,Fullerton, Califl, a corporation of California Application April 7,1955, Serial No. 499,940 13 Claims. (Cl. 241 -172) able about ahorizontal axis, containing one or more rotatable members whichcomminute the material in the rotor with a crushing action in responseto rotation thereof.

Still more particularly, the present invention contemplates a rotarymill wherein the rotor is a hollow cylinder rotatable about itslongitudinal axis, which is preferably horizontal, and wherein thehollow cylinder contains one or more rollers or roller memberspositioned with their longitudinal axes parallel to the longitudinalaxis of the cylinder, it being understood that whenever I referhereinafter to a roller or roller member, I am referring either to asingle roller in the cylinder, or to one of a plurality of rollers inthe cylinder, unless otherwise specified. r

The employment of a roller as the oornminuting L01 grinding means forthe material in the cylinder has numerous advantages over the employmentof such rotatable members as balls and some of these advantages will beconsidered at the present time, others being considered hereinafter.First of all, a roller provides line contact with the cylinder, asopposed to the point contact provided by a ball, and the roller has asmaller surface area than the ball for the same eifective contact areawith the cylinder. Since the roller has a smaller surface area, itprovides a substantial improvement in the proportion of the charge whichcan be recovered after the grinding operation, particularly'when thematerial. being comminuted has a strong tendency to adhere to surfaceswithin the mill. The advantage of a smaller surface is particularlyimportant when comminuting a mixture of materials some of which have astronger tendency to adhere -to the surfaces than others. Undersuchconditions, rotary mills employing balls may change the composition:of the'mixture being comminuted drastically,the

mixture recovered from the mill being low in the const'ituents havingstrong adhesivetendencies and high in constituents having low adhesivetendencies. Conversely,

that portion of the mixture which adheres to surfaces within the mill ishigh in constituents having a strong adhesive tendency and is low inconstituents having a low adhesive tendency. By minimizing the surfacearea for a. given effective contact area through the use of a roller,

adhesion, and therefore any change in the proportions of theconstituents of a mixture being comminuted, is minimized, this being animportant feature of the invention.

An important object of the present invention is to provide a rotary millhaving magnetic means for biasing the roller radially against thecylinder, the roller and cylinder r proximity to the cylinder to attainefficient magnetic a :tween the poles of the yoke and the roller withinthe preferably being horizontal andthe roller beingmagnetitional biasacting on the roller under such circumstances. I

More particularly, an important object of the invention is to provide amagnetic biasing means which provides a substantially closed magneticcircuit in order to attain maximum downward bias of the roller againstthe cylinder, thereby maximizing the effective weight of the roller andaccelerating the crushing action between the roller and the cylinder. Inthis connection it might be well to discuss another advantage resultingfrom the use of a roller, instead of balls, this advantage being that aroller can very easily be coupled into a magnetic circuit, whereas thisis difiicult or impossible to do with one or more balls.

Another object of the invention is to provide a mill wherein the rolleris coupled into a substantially closed magnetic circuit by means of ayoke belowthe cylinder,

the yoke having poles which are spaced apart longitudinally of thecylinder and which are positioned iniclose coupling between the yoke andthe rollen A related object is to provide the yoke with poles havingconcave cylindrical surfaces facing and complementary to the exterior ofthe cylinder so as to minimizethe gap becylinder.

With the foregoing construction, .it will be apparent that the yoke andthe roller within the cylinder provide a magnetic circuit which isclosed except for the gaps between the poles of the yoke and the roller,which gaps may be relatively small. Either or both the roller and theyoke may be permanent magnets. If only one is a; magnet, the other maybe of a relatively permeable metal,

such as soft iron or mild steel. If the roller isof relatively sofitmetal, it may of course be surface-hardened, plated or otherwise encasedin a hard outer layer. If the yoke is a magnet, it may, alternatively,be ofthe electromagnet rather than the permanent magnet type. It will beunderstood that when the hereinafter as a magnet, it may be eitherapermanent magnet, or an electromagnet.

Another object of the invention, and one of considerable importance, isto provide means for adjusting the magnetic field so as to vary themagnetic bias acting on the roller. According to the invention, this ispreferably achieved by providing an adjustable shunt in the magneticcircuit. In the preferred form of the invention, this is accomplished bymaking at leastone of the poles of the yoke movable longitudinally ofthe cylinder toward and away from the other pole so as to vary thespacing or gap between the poles. Either or both poles of the yoke maybemade movable longitudinallyof the cylinder by providing separate,longitudinally slidable gap or pole members conforming to the externalconfiguration of the cylinder as hereinbefore outlined. a i In case theyoke is an electromagnet, the magnetic biasing force may of course bevaried by varying theerr' ergizing current.

With the foregoing in mind, there are certain addition a1 advantages ofthe present invention in the preferred use of a single roller in thecylinder, as opposed to a plurality of rollers. One advantage is thatmuch closer coupling between the yoke and the roller can be attainedsince, with a single roller, the roller diameter can be a substantialpercentage of the internal diameter of the. cylinder so that the gapsbetween the yoke poles and the roller are minimized. In this way, theeifective weight of the roller is maximized to accelerate the grindingaction.

The minimum diameter of the roller then is determined by the minimum airgap, and also by the cross section 'and permeability needed to conductflux providedby Patented Apr. 21., 59

yoke is referred to the permanent magnet. The maximum roller diameter,

a plurality of rollers, so that adhesion, and changes in" theproportions of the constituents of a mixture due to adhesion, areminimized. Also, a single roller may be securely locked magneticallyagainst the side of the cylinder before and after grinding for saferhandling in case the charge being ground is an explosive material. Suchlocking, with assurance against relative motion of the rollers, would bedifficult or impossible with more than one roller. Another advantage ofa single roller is that" cocking or jamming, encountered when aplurality ofrollers is used, is eliminated. Also, the use of a singleroller eliminates the reduction in downward grinding force which mayresult when lateral friction between plural rollers produces a liftingforce thereon.

Among further objects of the present invention, it is desired to providea rotary mill wherein the cylinder is rotated about its longitudinalaxis in a horizontal position merely by placing the cylinder on spaced,parallel, horizontal rolls at least one of which is driven, the yokepoles being positioned between such rolls. In a small mill, the cylindermay serve as a container for transporting the charge being ground, bothbefore grinding and after grinding. It is merely necessary to place thecylinder, with the desiredcharge and the grinding roller therein, on therolls to ready the mill for operation.

Another object is to provide a cylinder comprising an open ended barrelhaving removable end-closures at one or both ends, and wherein themating surfaces of the barrel and the end closures diverge outwardlyaxially of the barrel at a small included angle so that the end closuresmay be pressed into the ends of the barrel to provide fluid-tightfriction seals or fits without the use of packing, seals, or the like.To attain this result, the half-angle of the conical mating surface maybe made as small as two degrees. A seal of this type is valuable sinceit is generally desirable to grind the charge of solid, granularmaterial in a suitable liquid vehicle, Le. a vehicle which will notdissolve or react with any of the components of the charge. In this waya smooth-flowing slurry is formed permitting accommodation of a chargeabout times as large as when dry materials are used that tend to pile upunder the roller. The vehicle may be water, but in some cases is asubstance such as a chloroform, methanol, etc., which may be destructiveto resilient seals made of rubber and like materials.

The foregoing objects, advantages and features of the present invention,together with various other objects, advantages and features thereofwhich will become ap parent, may be attained withthe exemplaryembodiment of the invention illustrated in the accompanying drawing anddescribed in detail hereinafter. Referring to the drawing:

.Fig. 1 is an isometric view of a rotary mill which embodies the presentinvention;

Fig. 2 is a sectional view taken along the arrowed line 2-2'of Fig. 1;and I Fig. 3 is an enlarged sectional view taken along-the arrowed line3-3 of Fig. 2 of the drawing.

In the drawing, the rotary mill of the invention, designated generallyby thenumeral 12, is mounted on a base 10, the mill being driven by areversible, variable speed, electric motor 14 mounted on the base. Themotor is controlled by a unit 16 also mounted on the base 10. Thecontrol unit 16 includes a panel 18 havingthereon an onoif switch 20, areversing switch -22, 'a, speed c'ontrol knob 24 and a signal light 26to indicate that the unit is in operation.

V A l 1 g 4 Considering the mill 1 2 in further detail, it includes twospaced standards 28 and 30 carried by the base 10;

Extending between and carried by the standards 28 and 30 are spaced,parallel, horizontal rolls 32 either or both of which are driven by themotor 14. In the particular construction illustrated, a sprocket 34 isconnected to one of the rolls 32 on the rear side of the standard 28,and a chain 36 engages this sprocket and a sprocket 38 on the motorshaft. In this construction, only one of the rolls 32 is driven, theother being an idling roll, although both rolls may be driven ifdesired.

Carried by the rolls 32 with its longitudinal axis horizontal is. acylinder 40 which, in the particular construction illustrated, isrotated about its longitudinal axis by the roll 32 having the sprocket34 connected thereto, the other, idling roll 32 being driven by thecylinder. The latter includes an open-ended barrel or tube 42, ofsubstantially non-magnetic material, into the open ends of which arepressed end closures 44, also non-magnetic,

having therein tapped holes 46 to receive threaded means, not shown, forpulling the closures from the barrel. The

mating surfaces of the barrel 42 and the closures 44": pressed thereintoare conical, diverging outwardly of the cylinder 40 at a half-angle ofthe order of two degrees.

With this construction, by pressing the closures 44 into the taperedends of the barrel 42 a predetermined distance,

consistently fluid-tight seals are obtained without the use of anyseals, or the like, this being an important feature in that it permitsthe grinding of solids in liquid vehicles which might have deleteriouseffects on conventional packing materials.

Disposed in the cylinder 40 with its longitudinal axis horizontal andparallel to the longitudinal axis of the that in general the rollerdiameter will be made smaller if a plurality of parallel rollers isused.

Carried by the base 10 below the cylinder 40 and between the rolls 32 isa yoke comprising a yoke member 50 and gap or-pole members 52 providedwith concave cylindrical surfaces 54 complementary to, facing, and inclose proximity to the exterior of the cylinder 40, the surfaces 54preferably having a common axis of curvature coinciding with the axis ofthe cylinder. Preferably, the pole members are made of a material ofhigh magneticv permeasibilty. With this construction, the gaps betweenthe pole members 52 and the roller 48 are minimized,

thereby establishing a substantially closed magnetic circuit through theroller 48, the gap members 52 and the yoke- 50. If a single roller isused, it will be apparent that the larger the roller diameter relativeto the inside cylinder diameter, the smaller will be the effective gapsbetweenthe roller and the pole members 52, and the better, therefore,the magnetic coupling therebetween.

In the particular construction illustrated, the yoke member 50 is shownas a simple U-shaped structure, but it will be understood that theconfiguration of the yoke may vary widely.

To provide a magnetic means for biasing the roller downwardly intoengagement with the cylinder 40, thereby increasing the effective weightof the roller and its efficacy in grinding, either or both the roller 48and the yoke member 50 may be magnets. Either the roller 48 or the yokemember 50 may then induce a magnetic flux around a magnetic circuit orloop comprising the roller, the yoke and the gap member, the circuitbeing closed, except.

magnetic material. Under these conditions, the yoke.

5 member 50 may be formed of a material, such as soft iron, having ahigh magnetic permeability in order to induce maximum flux in themagnetic circuit.

Alternatively, the yoke member 50 may be a magnet, either of thepermanent magnet type, or, by enclosing it in an energizing coil (notshown), of the electromagnet type. In the latter case, the roller 48 maybe made of a magnetic material of relatively high permeability, such asa mild steel, case-hardened to minimize wear, and the cylinder 40 may bemade ofnon-magnetic material to prevent shunting the magnetic fieldthrough the cylinder. For example, the barrel 42 and the closures 44 maybe made of stainless steel.

In order to adjust the magnetic field to vary the magnetic bias appliedto the roller 48, irrespective of whether the roller or the yoke member50 is a magnet, means 56 is provided for varying the spacing between thegap members 52, thereby providing a variable magnetic gap or shunt. Forthis purpose, the gap members 52 may be made slidable relative to and incontact with the end surfaces of the body of the yoke member 50 so thatthese gap members, or pole pieces, may be moved toward and away fromeach other. To vary the spacing between the pole members 52, two screws58 are carried by the standards 28 and 30 and have oppositely threadedportions 60 and 62 in threaded engagement with the respective poles. Thescrews 58 are interconnected to operate in unison by a gear train 64carried by the standard 30 and one of the screws extends through thestandard 30 and carries an actuating knob 66, the other screw alsoextending through the standard 30 and carrying an indicator 68 forindicating the relative positions of the poles 52. The indicator 68 maybe calibrated in any desired units, such as gap spacing, magneticbiasing force, or the like. It will be apparent that, in thisconstruction, the spacing of the poles 52 may be varied readily to varythe efiective weight of the roller 48, thereby to vary the rate at whichmaterial in the cylinder 40 is ground.

It will be understood that the slidable poles 52 are made of a materialhaving a high magnetic permeability. For example, they may be made ofsoft iron.

If the roller is a magnet, it may be desirable, in order to extend therange of adjustment of the magnetic bias, to make the magneticreluctance of the U-shaped member 50 large relative to the reluctance ofthe gap members 52 when the latter are in their closed positions. Thismay be done by slotting the member 50, reducing its cross-section, or byselecting a material of relatively low permeability. Alternatively, thebody of the member 50 may be omitted altogether, whereby the yoke willcomprise onlythe gap or pole members 52. In either case the magneticbiasing force is a maximum when the gap members 52 are in contact, andis reduced by separating the gap members.

0n the other hand, if the yoke member 50 is a magnet, then magneticbiasing force is a minimum when the gap or pole members 52 are incontact, and increases toward at maximum when the gap is opened. I

Although I have disclosed an exemplary embodiment of my inventionherein, it will be understood that various changes, modifications andsubstitutions, some of which have been suggested herein, may beincorporated in the embodiment disclosed without departing from thespirit of the invention as defined by the patent claims hereinafterappearing.

I claim as my invention:

1. In a mill for comminuting material, the combination of: a hollowcylinder rotatable about its longitudinal axis; means for rotating saidcylinder about its longitudinal axis with the longitudinal axis of saidcylinder substantially horizontal; a magnetic roller within saidcylinder with its longitudinal axis parallel to the longitudinal axis ofsaid cylinder; and magnetic yoke means external to and below saidcylinder and magnetically coupled to said roller to form therewith asubstantially closed magneticcircuit for biasing said roller downisnonmagnetic.

3. ha mill for comminuting material, the combination of: a hollowcylinder rotatable about its longitudinal axis; means for rotating saidcylinder about its longitudinal axis with the longitudinal axis of saidcylinder substantially horizontal; -a magnetic roller within saidcylinder with its longitudinal axis parallel to the longitudinal axis ofsaid cylinder; magnetic yoke means external to and below said cylinderand magnetically coupled to said roller to form therewith asubstantially closed magnetic circuit for biasing said roller downwardlyagainst said cylinder to increase the effective weight of said roller;and means for varying the magnetic bias applied to said roller. I

4. .jIn a mill for comminuting material, the combination of: a hollowcylinder rotatable about its longitudinal axis; means for rotating saidcylinder about its longitudinal axis with the longitudinal axis of saidcylindersubstantially horizontal; a magnetic roller within said cylinderwith its longitudinal axis parallel to the longitudinal axis of saidcylinder; magnetic means external to and below said cylinder andmagnetically coupled to said roller to form therewith a magnetic circuitfor biasing said roller downwardly against said cylinder to increase theeffective weight of said roller; and means for varying the magnetic biasapplied to said roller comprising adjustable magnetic gap means in saidmagnetic circuit, said gap means magnetically. shunting said roller.

5. In a mill for comminuting material, the combination of: a hollowcylinder; means for rotating said cylinder about its longitudinal axiswith its longitudinal axis substantially horizontal; a roller member insaid cylinder with its longitudinal axis parallel to said longitudinalaxis of said cylinder; and a magnetic yoke member magnetically coupledto said roller member to form therewith a substantially closed magneticcircuit for biasing said roller member downwardly against said cylinder,said roller member being longitudinally magnetizable and said yokemember being below said cylinder and having poles adjacent andmagnetically coupled to longitudinally spaced portions of said rollermember, one of said members being a magnet.

6. A mill as defined in claim 5 wherein said yoke member is a magnet.

7. A mill as defined in claim 5 wherein said poles have concavecylindrical surfaces which face said cylinder in close proximity theretoand which have a common axis of curvature substantially coinciding withsaid longitudinal axis of said cylinder.

8. A mill as defined in claim 5 wherein said means for rotating saidcylinder includes two spaced, parallel, substantially horizontal rollsrespectively located on opposite sides of said yoke member and on whichsaid cylinder rests with its longitudinal axis parallel to the axes ofsaid rolls, and includes means for rotating at least one of said rolls.

9. A mil-l as defined in claim 5 wherein said cylinder is nonmagnetic.

10. In a mill for comminuting material, the combination of: a hollowcylinder; means for rotating said cylinder about its longitudinal axiswith its longitudinal axis substantially horizontal; a roller member insaid cylinder with its longitudinal axis parallel to said 1011-gitudinal axis of said cylinder; and magnetic yoke means magneticallycoupled to said roller member to form therewith a substantially closedmagnetic circuit for biasing said roller member downwardly against saidcylinder, said magnetic yoke I means including a yoke member below saidcylinder and having poles located adjacent to and spaced apartlongitudinally of said cylinder and at least one of which is movablelongitudinally of said cylinder to vary the spacing between 'said poles,one of said one pole longitudinally of said cylinder.

11.1'A mill as defined in' elaim 10 wherein said yoke member is amagnet.

12. In a mill for comminuting solid material, the combination of: arotor; means for rotating said rotor; a rotatable memberin said rotor;magnetic means'forming with said rotatable member a substantially closedmagnetic circuit for biasing said rotatable member downwardly againstsaid rotor, said magnetic means including a yoke member external tosaid-rotor and magnetically coupled to said rotatable member andprovided with two poles at least one'of which is movable toward and awayfrom the other, one of said members being a magnet; and means foradjusting the magnetic field provided by said magnetic means, includingmeans for efieeting said movement of said one pole.

13., A mill as defined in claim 12 wherein said yoke member is a magnet.

References Cited in the file of this patent UNITED STATES PATENTS HyattMay 27, 1879 Wheeler Nov.,27, 18946 Ostwald Nov. 5, 1912' Wiswell Dec.5, 1916. Slocomb May 8, 1923 Ullrieh July 14, 1925'. Files Mar. 15, 1921Saflir Oct. 10, 1939 Pereney Aug. 20, 1940 Truax Dec. 29, 1942, PughMar. 21, 1950 FOREIGN PATENTS Germany July 29, 1924 Germany Sept. 30,1938

